As an interface for coupling multiple storage devices, there is SAS (Serial Attached SCSI). The SAS is able to couple multiple storage devices using an SAS EXPANDER (herein after referred to as “EXP”), and, in addition, the EXPs can also be cascade coupled.
A storage system, which uses SAS, can increase availability by using the EXPs to make a communication path to a storage device redundant. For example, Patent Literature 1 discloses technology for making a communication path to a storage device redundant using EXPs.